I think I've finally come up with a killer strategy that even the good folks at Smogon haven't. At least, it's not mentioned anywhere in their analyses. In my magnanimity, I will share it with you.
So. Step 1. Take a Drifblim. Train it for maximum HP. You'll probably want speed, too. Give it Substitute and Baton Pass. Anything that prevents the substitute from taking damage will help as well. Maybe Hypnosis. You might want to use the Flying Gem/Acrobatics/Unburden combo to boost its speed. Minimize might do the trick as well.
One of the buffs that Baton Pass can pass is Substitute. The substitute will retain the HP given to it by the original user of the move, but it always has the typing and defenses of the pokemon hiding behind it. Of all Baton Pass users, Drifblim's HP is the highest, making it an ideal choice for this setup. Pass the substitute to the pokemon with the highest defense: Shuckle.
Shuckle isn't dangerous, but taking one down even with status moves and other indirect attacks is a grueling effort. When the Shuckle is hiding behind a substitute which alone has 2/3 of the HP as the bug itself....
While hiding behind the substitute, a Shuckle can set up for just about anything. It's very likely to get the two turns needed to set up Trick Room and then Power Trick, turning it into the most powerful sweeper in the game (though the risk of running into priority attack users is high). If you do this, Rock Blast would probably be the more effective choice of attack, as it can deal with Sturdy and Focus Sash enemies. If you opt for a more defensive tactic, there's a good chance you'll get enough time to set up six layers of Double Team. Basically, anything that a Shuckle can normally do can be done better behind a gigantic Substitute.
There are drawbacks to this, of course. Substitute prevents contact effects from triggering, so a Rocky Helmet won't chip away at the opponent's HP. The substitute can't be healed with Leftovers (or, indeed, any other method), and the fact that you can't see the substitute's HP can hinder efforts to plan ahead. Roar, Whirlwind, and Perish Song all go through substitute, as well, which can put the kibosh on any setup you attempt. And it all goes to pot if your enemy can handle a Drifblim. But I think it has potential.